This invention relates to detection of faults in an automatic transmission operated by oil pressure.
A multistage gear type automatic transmission changes a motive transmission path via a combination of various gears inside the transmission, by selectively locking or unlocking plural friction elements such as clutches and brakes by oil pressure control.
Tokkai Hei 7-269685 published by the Japanese Patent Office in 1995 discloses an automatic transmission wherein valves for locking and unlocking frictional elements are individually provided between the frictional elements and an oil pressure pump. Further, a pressure switch for detecting variation of oil pressure supplied to each of the frictional elements is disposed in passages connecting the valves and the frictional elements. The operation of the valves is controlled by an electronic control unit.
In an automatic transmission where locking and unlocking frictional elements is performed by valve operation according to command signals from an electronic control unit, it is desirable to verify whether or not the transmission is working properly in accordance with the command signals, i.e., to determine by some method whether or not there is a fault in the automatic transmission. If locking and unlocking of the frictional elements is performed by oil pressure, some time is required until the locking and unlocking of the frictional elements by a valve operation is actually completed. There is therefore a risk of an incorrect determination if the presence or absence of a fault is determined within this transient period.
It is therefore an object of this invention to accurately determine the presence or absence of a fault in an automatic transmission.
It is another object of this invention to accurately detect an interlock tendency of an automatic transmission.
It is yet another object of this invention to rapidly eliminate an interlock tendency of an automatic transmission.
In order to achieve the above objects, this invention provides a fault determining device for an automatic transmission which changes over a gear position by selectively applying a fluid pressure to one of plural frictional elements while releasing a fluid pressure acting on the other of the plural frictional elements. The device comprises a pressure sensor which detects a fluid pressure acting on each of the frictional elements, a sensor which detects a completion of a gear position change-over of the automatic transmission, and a microprocessor. The microprocessor is programmed to determine a fault of the automatic transmission based on a detected fluid pressure, and prohibit determination of the fault when the gear position change-over is not complete.
This invention also provides a fault determining method for an automatic transmission which changes over a gear position by selectively applying a fluid pressure to one of plural frictional elements while releasing a fluid pressure acting on the other of the plural frictional elements. The method comprises detecting a fluid pressure acting on each of the frictional elements, determining a fault of the automatic transmission based on the detected fluid pressure, determining whether or not a gear position change-over of the automatic transmission is complete, and prohibiting determination of the fault when the gear position change-over is not complete.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.